Tanning process



- Patented May 3, 1938 UNITED STATES PATENT OFFICE;

- TANNING PROCESS Otto Biihm, Darmstmlt, Germany No Drawing. Application October 8, 1937, Serial No. 168,051. In Germany October 24, 1936 9Claims.

The invention relates to improvements in tanning processes and to the product obtained thereby.

I have found that valuable tanning agents are obtained if the water-insoluble phosphates of metals (the compounds of which are used for tanning) e. g. aluminum, chromium or iron phosphates are dissolved in oxalic acid.

It has previously been proposed to use alkali 10 phosphates in combination with aluminum salts and in alkaline solution for the preparation of leather. In this case, however, insoluble aluml= num phosphate and aluminum hydroxide only become deposited in the skin; an actual alumimun phosphate tanning does not occur. The

tanning is thus efiected rather by the additionally proposed simultaneous or sumequent use of vegetable tanning agents. Furthermore, it is also known to work insoluble metallic phosphates into hides through agency of an aqueous suspension. But this suspension penetrates into the hides to an even lesser degree.

Furthennore, it has been proposed when tanning with metallic salts and silicates, in order to stabilize the colloidal condition of the metal silicate tanning liquor, to use conjointly therewith acids which are more than divalent, such e. g. as phosphoric acid, in combination, if desired, with mono or divalent organic acids, such 3G asoxaiic acid. According to that proposal, only so much phosphoric acid is used as is just suificient to decompose a portion of the metalsalt into phosphate. Besides, the. amount of the oxalic acid used is too small to enable it to play any efiectiye role as a solvent for insoluble metal phosphates. From this it can only he assumed that these additions improve the keeping qualities of a metal silicate solution but it does not result that metal phosphates dissolved in oxalic acid yield a. valuable tanning agent.

Likewise, in producing leather it has been proposed toadd arsenic and phosphoric acid as well as their esters and salts to the solutions of inorganic salts such as'iron, chromium, and alumi- 1mm, but only in such amounts that they merely sufiice for decomposing a portion of the mineral tanning agent into phosphate insofar as any phosphate formation at all is concerned. This neither teaches that leather can he produced with dissolved metal phosphates alone nor that a solution involving a definite organic acid, e. g. oxalic acid, produces a valuable tanning agent.

The preparation of the tanning agents used in accordance with the present invention is efiected by dissolving the metal phosphate in oxalic acid.

It is known that water-insoluble aluminum phosphoto and iron phosphate can be dissolved in oxalic acid. Other metal phosphates moreover can also be dissolved, e. g. even chromium phosphate which according to the literature is difli- 5 cultly soluble. In the latter case, freshly precipitatedphosphate must be used and during the preparation care must be taken that no basic salt is formed.

Tanning by means of metal phosphates can be 10 carried out alone or combined with other types of tanning. Thus, for example, a pure white leather can be obtained by treating the hides with an oxalic acid solution of aluminum phosphate.

The phosphate tanning can be combined in a 5 liminary tanning is efiected with aluminum phos- 30 phate in oxalic acid solution, followed by an after treatment with synthetic tanning agents. If synthetic tawing and tanning agents are used it is possible to obtain a pure white leather in this manner which, due to the preliminary alumi- 35 .num phosphate tanning, is distinguished by possessing an especially good body;

The processin many important respectsv permits the replacement of foreign tanning agents by'cheaper and readily available domestic raw 40 materials without deleteriously afiectlng the quality of the leather.

Example i 199 kg. of neutral lamb skins are treated for six hours the first day and for iour hours the second day with:

4.6 kg. aluminum phosphate (anhydrous) 3.7 kg.oxalic acid (crystJ 5.6 kg. common salts 50.9 liters water then dried and prepared. A pure white leather is obtained. If a very soft leather is desired, it may then be after-treated with acid-resisting oiling agents. But the tanning can also be carcs ried on in the presence of egg yolk and flour as is customary in the manufacture of patent leather.

Example 2 100 kg. of neutral cattle skins are treated with: 5.7 kg. chromium phosphate (anhydrous) 7.4 kg. oxalic acid icryst.) 5.0 kg. common salt 100.0 liters water for so long a period until the tanning is finished. After drying, hard fats are burned in. A very solid chrome sole leather is obtained which has a full body.

- Example 3 a 100 kg. of neutral sheep skins are treated with:

11.6 kg. ferric phosphate ianhydrous) 12.1 kg. oxalic acid (cryst.)

5.0 kg. common salt 50.0 liters water until tanning is finished, then dried and prepared as lining leather. 1

' Example 4 The procedure is as for Example 1 but only preliminary tanning is eflected; an after-tanning is effected with:

100 liters water 5 kg. gambir After three hours the leather is removed and hung .up to dry. a

' Example 5 The procedure is carried out as in Example 1 but only preliminary tanning is eifected. An after-tanning is effected with: Y

100 liters water 40 kg. of a synthetic tawing tanning agent.

After six hours of treatment, the leather is hung up to dry. A very full, pure white leather is obtained in this manner which is suitable for pocket-book manufacturing purposes.

Example 6 The procedure is carried out as inthe case of Example 1 but'during the tanning 2.0 kg. of 30% formaldehyde are used condointly therewith.

Example 7 100 kg. neutral cattle skins are treated with: so kghsnlphitecellulose extract of 28-30 9.1 kg. aluminum phosphate (anhydrous 6.1 kg. oxalic acid icryst.) 25 liters water until tanning is finished. After being stored for two days they are after-tanned with a fresh liquor of the same composition and then dried. A sulphite cellulose sole leather is obtained in this manner. The leather in dried condition can also be filled with an-acid silicic acid solution filler. This produces a very solid, compact sulare used for tanning purposes. This impregnatina process is particularly suited for rendering leather more solid. The process is primarily adapted for rendering leather more solid which is intended to be used for sole leather purposes. Thus, for example, bark tanned leather, chrome tanned leather or sulphite cellulose leather may be treated with a solution of aluminum phosphate in oxalic acid. But this method may also be used for various kinds of upper leathers which for various reasons are to have a greater stiffness.

Substances like grape sugar, sulphite cellulose extract, and water soluble fats, may be added to the oxalic acid solutions of the metal phosphates in order to increase the elasticity of the grain.

If desired, the impregnation process'involving the use of the oxalic acid solution of water-insoluble metal phosphates may be immediately followed by impregnation with known impregnating agents e. g. colloidal. siliclc acid.

The process of the invention has the great advantage that it does not deleteriously afieet the permeability of the leather to air and that it increases the water-proof qualities thereof.

If barked tanned and extract filled sole leather is subsequently treated with aluminum phosphate in oxalic acid, a thorough fixation of the uncombined tanning agent takes place. The same can be effected by after' treatment 01' sulphite cellulose leather with aluminum phosphate and oxalic acid. This also produces a leather having good cut and high stlfiness.

Various embodiments are herewith:

Example 8 100 kg. neutral cattle hides are treated with:

50 kg. sulphite cellulose extract of 28-30" B. 25' liters water until tanning is completed. 7 After this time, the leather is stored for two days on the horse and then treated for two days with a fresh liquor of:

then stored for one day-on the horse, and then hung in the air.

This leather is treated with a solution of:

2.7 kg. aluminum phosphate (anhydrous) 2.2 kg. oxalic acid (cryst.)- 7.0 liters water y The leather is stored over night on the horse, then after treated with the following solution:

10 kg. sodium silicate solution having 25% SiO:

4 liters formic acid 15 liters water After the entire liquor is absorbedthe leather washed off on both sides, oiled with linseed oil and dried.

trample-9 kg. of neutralized chrome leather which has been hung in the air is treated for one hour in a barrel with:

14.5 liters water 5.5 kg. aluminum phosphate ianhydrous) 4.0 kg. oxalic acid (cryst.)

6.0 kg. sulphite cellulose extract containing 44% of tannin until all of the liquor is absorbed. After standing all night, the leather is stored on the horse.

given in the examples 9,116,880 then after-treated to fix the same, with a soluis hung in the air and then after-treated (pertion of 10.0 kg. sodium acetate 10.0 liters water Example 10 100 kg. moist and bark tanned sole leather which has been hung in the air is treated with a solution of:

7.3 liters water 2.7 kg. aluminum phosphate (anhydrous) 2.0'kg. oxalic acid (cryst.)

3.0 kg. sulphite cellulose extract containing 44% tannin Example 11 Dry chrome sole leather is immersed for two hours in a solution of 17 parts of ferric phosphate, 100% 18 parts of oxalic acid 36 parts of water at C.

18 parts of 10% ammonia solution 11 parts of grape sugar stored on the horse over night, then oiled on both sides, dried, and prepared as usual.

Example 12 The procedure is carried out as in Example 'I but without aluminum phosphate and without oxalic acid. After the tanning is finished the leather kg. of hide weight) with a solution of:

- The treatment is continued until all of the liquor is taken up. Thereupon the leather is stored for several hours, then set out by machine and by hand, and oiled on the grain side, hung up and dried. The filling procedure may be effected twice if desired.

I claim:-

1. Tanning process characterized by treating skins or leather with oxalic acid solutions of water-insoluble phosphates of metals the compounds of which are used for tanning purposes.

2. Tanning process characterized by treating skins or leather with an oxalic acid solution of aluminum phosphate.

3. Tanning process characterized by treating skins or leather with an oxalic acid solution of chromium phosphate.

4. Tanning process characterized by treating skins or leather with an oxalic acid solution of iron phosphate.

5. Process according to claim 1, characterized by the feature that substances are added which are adapted to increase the elasticity of the grain.

6. Process according to claim 1, characterized by the feature that sulphite cellulose extract is added.

'7. Process according to claim 1, characterized by the feature that grape sugar is added.

8. Process according to claim 1, characterized 35 by the feature that a water soluble fat is added.

9. Leather produced according to claim 1.

- oT'ro RGHM. 

